This invention relates to a compressor including a slide valve with a hot gas bypass incorporated in the slide valve.
Compressors and the vapor compression systems in which they are installed must be able to operate at their full capacity and at some reduced capacity, depending on the application and environmental surroundings (i.e. the outdoor temperature, temperature of media being cooled, and volume/flow rate of the media being cooled). It is desirable to have a compressor/system that can continuously operate at the smallest possible percentage of full load capacity to avoid on/off cycling of the compressor/system and to avoid the temperatures swings in the media being cooled that will result from the on/off cycling.
As a result of the need to operate at less than full load capacity at certain times, compressors must have a method of varying the amount of refrigerant that they compress. Screw compressors, in many cases, use slide valves as their unloading mechanism. As the slide valve moves toward the discharge end of the compressor, the compressor's displacement or swept volume decreases, which in turn reduces the amount of refrigerant that the compressor draws in, compresses and discharges. It is desirable to have a screw compressor achieve the lowest possible percent of full load while minimizing the amount the slide valve has to travel toward the discharge end of the compressor
Screw compressors may also use “lift” or “poppet” valves, suction throttling, or hot gas bypass, internally or externally applied, to achieve partially unloaded or unloaded operation. Hot gas bypass, in particular, vents refrigerant (that has already been compressed) from the discharge plenum or discharge line back to the suction plenum thereby displacing some of the refrigerant that would have otherwise entered the compressor through the suction flange. The bypass line(s) requires a solenoid valve to control the unloading through the bypass line. All of these methods lower the amount of refrigerant circulating through the vapor compression system with varying amounts of efficiency. If any of these methods are used in conjunction with a slide valve to further reduce the amount by which the compressor unloads, they will require additional compressor/system controls. Therefore, there is a need in the art for a slide valve that allows for greater unloading of the compressor but does not require increasing length or size of the compressor or additional unloading controls.